This invention in general relates to a centrifugal machine with a suspended floating group and an overhanging drum, specially applicable to washing-centrifugal machines designed to high centrifugal speeds with high G factors, in which said floating group essentially comprises a wrapping bin to contain and/or to collect a bath, a drum having bored walls for a load of material to be centrifuged mounted so that it can rotate within said wrapping bin, and a motor fixed on the wrapping bin and connected to said drum to rotate it, in said machine a suitable ratio of counterweigh masses provides as result a reduction of structural stresses at the floating group which allow a light construction thereof and namely of the wrapping bin.
The method of withdrawing water from a wetted material through centrifugation is well-known and it is thoroughly used, for example, in the either industrial or home sector of clothes washing, because of its high performance of withdrawal with relation to the power expense compared with other methods. In this sector, it is very usual to use machines capable to wash and subsequently to centrifuge a load of clothes introduced in a drum having bored walls mounted so that it can rotate within a wrapping bin capable to contain succeeding bathes of washing and rinsing and to collect the rests of said bathes extracted from the clothes during an end centrifuging step. For this, one or more motors are connected to the drum to successively rotate it at different speeds according to the washing, rinsing and centrifuging steps, driven by programmable control means.
It is very typical that the drum is situated so that during the operation, its hinge axis is horizontal or slightly inclined with respect to the horizontal, and that it has a loading/unloading mouth at an axial end thereof, coinciding with an opening of the wrapping bin. This is specially advantageous in industrial machines designed to heavy loads of clothes in which the radial loading mouth would result of a very complex access because of its great height. The existence, however, of said loading/unloading mouth at one end of the drum obliges to support it overhanging from the axial end opposite to the loading/unloading mouth, by means of a driving shaft integral with the drum rear wall, supported and guided by bearings housed within a bearing box fixed on the wrapping bin. This arrangement, although it results very favourable from an ergonomic standpoint, produces stronger bending moments on the driving shaft and transmits stresses on the bearings stronger than if the drum had been supported and guided at both ends. In addition, when the drum rotates at such a speed that it produces a centripetal acceleration on the clothes load higher than 1 G (G=earth gravity acceleration=about 9.8 msxe2x88x922), such as during a centrifugation, where 200, 300 and even over 400 G factors are reached, the clothes are radially applied against the drum wall at a random relative given position, which virtually does not vary while the effect of said speed is kept. Said random relative position has a very high probability to produce a centre of the masses of the clothes load misaligned with respect to the drum centre line, which is aligned with the driving shaft and therefore the centre of the masses of the drum and clothes load group will also be shifted with respect to said centre line. In these conditions, said drum and clothes load group will tend to rotate with respect to said misaligned centre of masses of the drum centre line, or with other words, the drum centre line will tend to rotate about an actual rotation axis different from the centre line, producing a wellknown vibrating motion which is transmitted to the whole floating group. Said vibrating motion is generally decreased adding counterweights and it is absorbed by said floating group system of suspension, formed by springs and vibration eliminators linked to a machine frame or bench.
U.S. Pat. No. 2,525,781, of Jey Grant De Remer, applied for on Sep. 15, 1944, discloses an equilibrating system for rotating bodies, specially applicable to clothes washing-centrifugal machines, based on providing one or more annular chambers partly filled with a fluid, located on different areas of the drum and coaxial with respect to the centre line thereof. Each of said chambers is formed by substantially parallel external and internal concentric annular walls and substantially parallel sidewalls, and there exists within them deflecting means which tend to drift the fluid contained within the chambers without preventing a free distribution thereof. When the rotation speed of the equilibrating ring and the drum is such it produces a G factor over 1 and over the floating group resonance frequency, the fluid of the interior of the equilibrating chamber is applied against said external wall thereof, which is coaxial with respect to the drum centre line, at same time it defines an internal circular horizon coaxial with respect to the actual rotation axis, a centre of masses of said fluid being created which is shift with respect to the actual rotation axis in a direction just opposite to the shift of the masses centre of the clothes load and therefore equilibrating it. Jey Grant De Remer discloses in said patent U.S. Pat. No. 2,525,781 that the optimum equilibrated situation is produced when the radial height at the point of the fluid maximum radial height within the equilibrating chamber is twice the distance between the centre line and the actual rotation axis, that means, twice the amplitude of the machine vibrating motion, and when the circle of the chamber external wall and the circle of the fluid circular horizon are tangent at a point diametrally opposite to the maximum height. Jey Grant De Remer also demonstrates that it is more favourable to arrange two concentric equilibrating chambers instead of a single chamber having a height equivalent to the sum of the other two, with same width and an amount of contained fluid equivalent to the other two together.
In said patent U.S. Pat. No. 2,525,781, however, of Jey Grant De Remer, only the drum equilibrating is discussed without discussing, at any moment, the dynamic effect of the xe2x80x9cpitching motionxe2x80x9d that the masses of clothes load and of the fluid rings produce on the floating group, therefore the position of the equilibrating fluid rings on the drum appears as a minor matter, obeying more to formal or construction criteria than to dynamic requirements.
Said dynamic effects of xe2x80x9cpitching motionxe2x80x9d consist in a drum dynamic shift, and therefore of the floating group, which has a different amplitude at each of its ends, being generally, in this kind of machines, of a larger amplitude at the drum end farther away from the bearings.
In the state of the art shiftable solid mass rings are known, for example for an embodiment of SKF company, which includes solid balls, generally of steel, enclosed in an annular circuit, which, when the group is subject to an misaligned rotation which produce G factors over 1, are concentrated being situated at the area of said annular circuit farthest from actual rotation axis. In the most recent embodiments, as the one disclosed in patent U.S. Pat. No. 5,813,253, in order to prevent noises produced by the balls colliding with each other when rotating at low speed, it is provided a locking device formed by cages which match the balls two by two, in said cages there is a spring-loaded pin, which at G factors under 1, pushes the pin in order it is inserted in holes arranged on the internal track of the annular circuit. When G factors are substantially over 1, the pin mass itself generates a centrifugal force which gets over said spring releasing the cage with its related pair of balls, which then shift until they concentrate at said area farthest from the actual rotation axis.
Although said ball device showed to be very effective as for its balance compensating effect, the requirements of accurateness of its complex construction make its cost very high, over all if it is borne in mind that, in an application as the one proposed, said device will sustain continuous dipping on the baths of the washing and rinsing processes, making its implementation absolutely unworkable.
Patent DE-A-1610177, of Siemens-Electrogerate GmbH, applied for on Oct. 6, 1967, discloses a clothes washing-centrifugal machine in which a single equilibrating fluid ring is arranged at the end of the drum closest to the bearings. The ring comprises a relatively large capacity chamber and means to partly fill with fluid or to empty said chamber depending on the washing and centrifuging steps. The drum has a slightly conical shape, its diameter decreasing when moving away from the bearings, which favours an advantageous accumulation of the clothes load towards the wider area, that means, towards the area closest to the bearings. The arrangement of the fluid ring, however, in this wider area does not favour masses dynamic balance.
Currently, the generalized practice of the manufacturers of washing-centrifugal machines consists in placing solid counterweights fixed on the wrapping bin and, to a lesser extent, on the drum. Because the heaviest elements of the floating group, that means, motor, bearing box, bearings, drum reinforced rear wall and wrapping bin, are concentrated at the rear end, or farthest from the floating group loading mouth, the solid counterweighs are mainly located at the front ends or closest to the loading mouth, of the drum and the bin. To fix counterweights on the drum, however, has the drawback that these will sustain the washing baths, which means associated problems of corrosion which oblige to use anti-rust construction materials and elements which results in a high cost. In addition, to place large additional masses on the rotating drum shows a drawback from the standpoint of an increase of the moment of inertia which impairs the drum accelerations. Therefore, it is a generalized practice to place large counterweigh masses at the front part farthest from the bearings, of the wrapping bin.
For the purpose of this description, often the terms xe2x80x9cfront and rearxe2x80x9d will be used referring to parts of the wrapping bin or the drum as those parts respectively farthest or closest to the bearings.
On the market, a clothes washing centrifugal machine is known of the company Maytag Corporation which matches a large counterweigh fixed at the front part or the farthest from the bearings, of the wrapping bin with two fluid equilibrating rings, such as the disclosed in patent U.S. Pat. No. 2,525,781, concentric on the drum front face, at an external peripheral area of the loading/unloading mouth. The advantage of the fluid rings is that, as it was explained above, with an actual fluid mass relatively small they provide an effect as for centrifugal force equivalent to a very higher mass, so that the wished effect of balance is achieved without excessively increasing the moment of inertia of the drum.
However, the large counterweigh mass fixed at the part of the bin farthest from the bearings provokes, as it will be explained below, great stresses on the floating group structural elements, namely on the driving shaft, bearing box, bearings, drum and wrapping bin reinforced rear walls, and in general all the remaining walls of the drum and the bin, which oblige to construct them with high mechanical strength requirements which results in an heavy construction. Said heavy construction, concentrated at the rear part of the floating group, increases in turn the amplitude of the vibrating effect at the front part, which makes advisable to increase even more the counterweighs on said front part and so on.
An aim of this invention is to provide with a centrifugal machine having a suspended floating group and an overhanging drum, applicable to washing-centrifugal machines designed to high-speed centrifugation with high G factors, in which a suitable distribution of the counterweigh masses results in reducing the structural strengths which allows the construction of the main elements of said floating group, such as the wrapping bin, drum said bearing box, bearings, and said driving shaft, with mechanical strength requirements, either for the shape, materials or components, significantly lower with respect to those necessary without said suitable distribution of the masses, for same performances of high-speed centrifugation, and therefore with lower costs.
This aim is achieved, according to this invention, by transferring a significant part of the counterweigh associated to the front part of the wrapping bin to the front part of the drum, so that the mass, either actual or equivalent obtained by fluid rings, of said counterweigh associated to the drum is at least 55% the sum of the masses of the counterweigh itself associated to the drum and the counterweigh associated to the wrapping bin.
It has to be pointed out that for the purpose of simplifying the language, in this description often the expression xe2x80x9cactual massxe2x80x9d and xe2x80x9cequivalent massxe2x80x9d counterweigh for the drum refers, respectively, to a generally solid counterweigh, with a mass of a given magnitude and centred on the centre line of the drum and to a counterweigh having a very lower magnitude and in the form of one or more fluid rings which, when rotating at such a speed it produces a G factor over 1 and over the floating group resonance frequency, it is misaligned at a distance very higher than the amplitude of the dynamic shift of the floating group producing dynamic effects equivalent to those of said mass of a given magnitude.
In fact, the present inventors found, through the theoretical analysis corroborated by actual practical tests and by means of simulation computer programs, that the effects as for a dynamic balance produced by a counterweigh fixed on the front part of the wrapping bin are equivalent to those produced by a counterweigh having same mass fixed at the front part of the drum (supposing that both are located at same distance from the bearings), while transferring said counterweigh from the front part of the bin to the front part of the drum, every part of the wrapping bin, such as the bearing box, the bearings, the shaft and the rear part of the drum are released from the structural stresses attributable to the transmission of stresses carried out by said counterweigh. If, in addition, by virtue of the dynamic properties offered by the drum rotation, fluid equilibrating rings are used which have an actual mass very lower than the mass equivalent to the transferred counterweigh, the structural stresses sustained by the drum also decrease. These decreases of structural stresses make possible a lighter construction of the floating group elements, which alleviate the masses concentration at the rear end thereof, which means that the mass, either actual or equivalent, of the counterweigh associated to the front part may also be smaller, which in turn reduces the structural stresses and so on. Therefore, said transfer of masses results very advantageous and is translated in an important decrease of the costs, because, for example, the wrapping bin can pass from a stainless plate welded construction,usual in machine having an over 7 Kg capacity and centrifugation values of 250 G or over, to a construction by plastic injection moulding, integrating the bearing box which otherwise can probably be a part of steel casting and the driving shaft and related bearings would be much smaller and therefore also cheaper. By providing a generally lighter weigh to the machine of this kind also involves an easier transport and lower requirements as for the structural strength of the place where they are installed.
The suspension system is capable to absorb a given amplitude of vibration of the floating group, therefore a relatively strong vibrating movement does not mean a drawback from the mechanical standpoint while it is within the interval capable to be absorbed by the suspension. Now then, for the reasons above explained, said amplitude of the vibrating movement is generally higher at the front part of the floating group than at the rear part, which entails higher flexibility requirements at elastic connections usually arranged between the door of the frame and the loading/unloading mouth at the front part of the floating group, in addition to an unpleasant visual feeling for the user. It is therefore advisable to decrease said vibration amplitude arranging a given counterweigh mass on the front end of the wrapping bin in addition to the counterweigh mass arranged on the front part of the drum. The present inventors determined that from a relation of the counterweigh mass associated to the front part of the drum with respect to the sum of the counterweigh masses respectively associated to the front part of the drum and to the front part of the bin of 55% the advantageous effects of said masses transfer object of the construction principle of this invention are sufficiently important to allow said light construction of the floating group.